b4's `misc/vim` directory provides ftdetect/ftplugin/syntax files that
highlight the `b4 review` reply editor (activating for *.b4-review.eml
buffers). Package them as a Vim/Neovim plugin, sourced from the b4
package's `passthru.src-misc` so the version stays in lockstep with b4
itself, following the notmuch-vim/hurl precedent.
Assisted-by: Claude Code (Claude Opus 4.8)
